Modeling phosphorus losses to subsurface drainage under tillage and compost management

While agriculture consumes 80–90 % of the world's annual phosphorus (P) production, only 20 % is utilized effectively by plants. Efforts to reduce agricultural P losses through various best management practices (BMPs) including no-till and organic fertilizer have helped substantially mitigate P pollution. The objective of this study is to investigate the long-term P losses through tile drainage as affected by tillage and compost amendment using the newly-developed RZWQM2-P model. We found that the model accurately simulated field-measured annual drainage water flow, as well as annual particulate P (PP) and total P (TP) losses in tile drainage, although it underestimated dissolved reactive P (DRP) when compost was applied. Long-term simulation results showed that tile drainage flow was negatively correlated with tillage intensity (TI, between 0 and 1), and tile-drainage-borne P losses were negatively correlated with TI and manure/compost P mix efficiency (ME, between 0 and 1) with soil after tillage. Specifically, when TI increased from 0 (no-till) to 0.93 (moldboard plow), drainage flow, DRP, and PP losses decreased by 11.49 %, 48.12 %, and 30.29 %, respectively. Similarly, when ME increased from 0 (no-till) to 0.5 (Tandem Disk), DRP and PP losses through drainage flow reduced by 53.98 % and 30.95 %, respectively. ME was not directly associated with drainage flow volume in the model. Overall, the RZWQM2-P model can accurately simulate PP and TP losses on an annual basis, although DRP loss prediction still needs to be improved, and it can be used as a tool to evaluate tillage effects on P loss from tile-drained agricultural land under manure or compost application.